1. Field of the Invention
The present invention relates to the control of bandwidth in a packet-based data system.
2. Description of the Related Art FIG. 1 shows a schematic block diagram of a conventional multipoint-to-point packet-based data system 100, such as those used for computer networks and telecommunications systems, in which a base station 102 communicates with a number of network nodes referred to here as network interface units (NIUs) 104. In the downstream direction, transmitter 106 of base station 102 transmits packets of data to the NIUs 104. In the upstream direction, one or more of the NIUs 104 transmit packets of data to receiver 108 of base station 102. In one possible implementation, the data packets are interleaved in the upstream and downstream directions using a time division multiple access (TDMA) scheme. The base station and the NIUs are the various nodes in the data system, with the base station controlling the bandwidth in the network (e.g., the allocation to the various NIUs of time slots for upstream transmissions).
When used, for example, in a telecommunications application, each NIU 104 in data system 100 provides the interface to the data system for a telephone or other node in the network, and base station 102 may be a switch in a central office or other component that communicates with multiple NIUs. In such an application, each NIU 104 is capable of sending control messages to base station 102. Control messages are information exchanged between NIUs and the base station that allow the base station to properly monitor and maintain communication channels within the allocated bandwidth of the communication system. The control messages may be embedded, for example, in the packets sent from the NIU to the base station in the upstream direction using the well-known slotted ALOHA technique. When a phone call is to be terminated at a particular NIU 104, the base station 102 assigns a particular channel for that NIU to use for its upstream communications. However, when a particular NIU wants to initiate a phone call, it must send an upstream control message to the base station requesting bandwidth for the phone call. Since the NIU does not have a particular channel already assigned, it may arbitrarily or randomly select a channel for its bandwidth request message. This upstream message may collide with one or more other upstream messages being sent to the base station from one or more other NIUs in the same channel, leading to corrupted messages which the base station cannot accurately process.
According to the slotted ALOHA technique, a collision/back-off algorithm is followed when two or more NIUs attempt to send such control messages at the same time to ensure successful NIU-to-base-unit message communications. One conventional collision/back-off algorithm calls for each competing NIU to retransmit its bandwidth request after delaying for a random period of time. Unfortunately, when many NIUs attempt to send control messages at the same time, the resulting collisions, retries, and further collisions may effectively block almost all upstream message transmission. This is undesirable, since such an overload condition could in theory happen during exceptionally high call volumes, which would limit the ability of the system to allocate bandwidth to the NIUs (e.g., providing dial tone to new calls for telephony systems).